Comparison processes on visual mental images.

Three experiments were conducted to test whether visual mental images and visual perceptual representations possess equivalent structural properties and undergo functionally equivalent comparison processes. In Experiment 1, subjects were required to perform a same-different letter classification in which the two letters were shown in succession. The first letter in the pair either was actually presented (perceptual condition) or had to be actively generated (imaginal condition). Both conditions showed that (1) response latencies for different decisions decreased as a function of the degree of difference (segment effect), and (2) same decisions were faster than the fastest different ones (fast same effect). In Experiment 2, the imaginal condition only was employed, but no imagery instructions were given and very strict time constraints were assigned. In spite of these restrictions, subjects apparently generated and used visual images, as attested by the fact that the results were comparable to those of the previous experiment. In Experiment 3, three experimental manipulations were introduced to prevent the use of visual images. Such manipulations proved effective, as shown by the disappearance of the segment effect. It was concluded that in the visual modality images and percepts are equivalent in structure and are processed in a very similar way. © 1988 Psychonomic Society, Inc.